The ImmPRESS polymerized reporter enzyme staining system uses novel conjugation and micropolymer chemistries to create a highly sensitive, ready-to-use, one-step, non-biotin detection system for immunohistochemistry and immunocytochemistry staining. This unique micropolymer of highly active enzyme (peroxidase or alkaline phosphatase) is attached to our affinity purified secondary antibodies, producing reagents with outstanding sensitivity and low background. The peroxidase micropolymers of the ImmPRESS HRP polymer reagent limit steric interference and provide enhanced accessibility to the target, avoiding the disadvantages of other polymer systems that use large dextrans or other macromolecules as backbones. The result is crisp, strong staining of antibody targets, especially nuclear and membrane antigens (such as Ki67, estrogen receptor, bcl-2, CD3, CD8 and CD10) and greater sensitivity than other polymer systems.